The introduction of the compact digital audio disc (CD) has resulted in a true advance in audio program playback technology. The CD contains a digitally encoded rendering of the program audio signal transferred onto a disc of polycarbonate plastic by molding or stamping. The encoded surface is then uniformly coated with aluminum and coated with a sealant such as lacquer. The aluminum sputtering on the stamped surface creates a reflective surface which is read by a laser beam through the opposite side of the polycarbonate disc. The laser reflection is converted to an audio signal which is heard through standard audio playback components.
The CD is considered a substantial advance over the vinyl record album for several reasons. First, the CD is capable of storing considerably more audio program material per unit area than a vinyl album. This permits the use of a much smaller disc for the presentation of recorded music (hence the term "compact" disc). Next, the ability to retain an audio program capable of being digitally decoded results in a substantial improvement in signal to noise ratio and program fidelity when compared with a vinyl record. Finally, the use of a laser beam as the transducer results in little if any degradation of the CD playing surface during playback. The playback properties of the CD will thus remain essentially unchanged, even after extensive use. However, there are factors which interfere with the reflection of the laser beam from the aluminum sputtered surface and adversely affect CD playback performance. Several such factors are scratches, dust, and fingerprints.
Because of the need to protect the surface of the CD through which the laser reflects, i.e., the optical surface, various CD storage devices have been developed to address this problem. By far the most prevalent storage device is a package known as the jewel box. The jewel box consists of two pieces of molded polycarbonate which are hinged along a common side to permit the opening of the box as one would open a book. Snap fit inside one of the polycarbonate pieces is a styrene tray with a center hub which engages the center aperture of the CD. The jewel box is slightly larger than the 12 cm diameter of the CD. Though the jewel box serves to protect the CD, the box itself suffers from certain disadvantages. The box is difficult to open, and it is difficult to remove the CD from the centered hub without bending the CD. The jewel box is relatively fragile, resulting in breakage of the hinges or the polycarbonate pieces themselves when accidentally dropped. Finally, the jewel box is expensive to manufacture because of the three piece construction and the need to manually assemble the parts.
One alternative to the jewel box for use in after-market storage of the CD is a device known as the CD Jockee produced by DataPax, Kennewick, Wash. The CD Jockee is a CD carrying case which opens into an A-frame shape and has eight two-sided, clear vinyl pockets that can carry up to 16 compact discs. The pockets are connected in an overlapping fashion, such that only a small portion of the discs underlying the top disc can be seen. The individual pockets have a clear vinyl front to permit viewing of the side of the CD containing identifying printing, and a velour back which contacts the optical surface of the CD. The reverse side of each pocket can hold the printed graphics accompanying the CD stored on the front, or alternatively it may be used to store another CD. The CD Jockee has the disadvantages that when the compact discs are displayed, the discs themselves are exposed to dust because of the open top access to the discs. Further, when displayed, one must typically flip through each pocket to find the desired CD because only a small portion of the printed surfaces are visible. Also, the velour surfaces generate relatively large amounts of lint which can accumulate on the optical surfaces of the discs.
Yet another alternative to the jewel box is the CD storage container described in U.S. Pat. No. 4,850,731, which is incorporated herein by reference. The CD storage container described therein for single discs is comprised of a backing sheet, a nonwoven fabric joined to the backing sheet, a transparent front sheet over the nonwoven fabric and a pocket-forming sheet which-extends over the transparent front sheet to form a flap which protects both the stored CD and the graphics. Upon folding back the flap, one can remove the CD by simultaneously accessing the aperture and edge of the CD. This allows removal of the CD without the need to touch the optical surface. The '731 patent also discloses a sheet which can store at least two discs thereon. The CD is stored in a pocket which leaves exposed the aperture and a portion of the edge of the CD to permit removal without touching the optical surface of the CD. Though both the single disc and multiple disc storage containers provide excellent protection for the CD, the containers have certain limitations. The single CD container has a flap which overlays the entire storage area. The length and weight of the flap helps to ensure that the portion of the CD not in contact with the transparent front sheet nonetheless remains covered. However, to be effective the flap requires the use of excess plastic film. The multiple CD storage container provides relatively good protection for the CD, but doesn't cover the entire printed surface, relying on adjacent pages to provide coverage.